1. Field of the Invention
This invention relates to a liquid developing apparatus for developing an electrostatic latent image recorded by an electrophotographic method or an electrostatic recording method by use of a liquid developer.
2. Description of the Prior Art
There have been proposed various kinds methods of applying a liquid developer to the surface of a latent image carrier. They are roughly classified into the following four kinds methods of: (1) immersion development in which the latent image carrier is immersed in a liquid developer, (2) shower development in which the latent image carrier is exposed to a shower of liquid developer, (3) roll development in which a liquid developer is supplied to the surface of a developing roller capable of holding the liquid developer and the developing roller is put into contact with the surface of the latent image carrier, and (4) jet development in which a jet of liquid developer is applied to the surface of the latent image carrier.
In the development of an electrostatic latent image recorded by an electrophotographic or electrostatic recording method, it is a general demand to develop a high quality image without uneven development at as high a speed as possible. The aforesaid known developing methods have drawbacks as mentioned hereinbelow, respectively.
In the immersion development, a development elecrode is generally used in order to reduce an edge effect. However, since the latent image carrier is simply immersed in the liquid developer and there is no specific means for applying a large amount of fresh liquid developer to the surface of the latent image, the developing speed is low and there is a tendency that the image is unevenly developed.
In the shower development, it is difficult to supply a large amount of liquid developer uniformly to the surface of the latent image.
In the roll development, it is difficult to uniformly apply the liquid developer to the whole surface of the developing roller. Further, in case of developing the image with the developing roller pressed on the latent image carrier, the image is likely to be deformed by the contact with the roller. Furthermore, since the amount of the liquid developer applied to the latent image carrier is limited to the amount held by the developing roller, a large amount of the liquid developer cannot be applied.
In the jet development, it is possible to apply a large amount of liquid developer to the latent image carrier as compared with the above methods. Accordingly, this method is widely adopted. However, this method needs improvement in the uniform application of the large amount of liquid developer to the latent image carrier. There have been suggested various improvements in this connection, which are however still not sufficient to solve the problem.
In general, the development of an electrostatic latent image is conducted by use of a liquid developer in which toner particles having electric charge are dispersed in an insulating liquid. In order to obtain images of high quality with uniform development at a high developing speed, it is important to supply a large amount of liquid developer having uniform characteristics to the surface carrying the latent image as uniformly as possible. Nonuniform supply of the liquid developer will result in uneven development or lines in the developed image as often experienced.
Another important point in the liquid development for obtaining a uniform image is to remove the used liquid developer from the developing area as quickly as possible and to supply a fresh liquid developer thereto.
In more detail, in the development of an electrostatic latent image, charged toner particles dispersed in a carrier liquid stick to the surface of the latent image carrier. At this stage, particles contained in the liquid developer close to the surface of the latent image carrier stick to the surface with priority. Consequently, as the development advances, the charged particles in the liquid developer close to the surface of the latent image carrier are reduced in number and the composition or characteristics of the liquid developer close to the surface are changed from those of the fresh liquid developer before being used for development. In the development, since the latent image is developed while being moved at a speed relative to the liquid developer, the liquid developer having less number of charged particles moves to other parts of the latent image and is used for development again, where the development is conducted with a smaller number of charged toner particles resulting in uneven development.
It is preferable that the liquid developer used for developing a part of the electrostatic latent image not be supplied to other parts of the latent image for developing other parts as described above. It is, therefore, important that the liquid developer used for developing a part of the latent image is quickly removed from the surface of the latent image and a fresh liquid developer is supplied thereto. This is obviously effective also for accomplishing high speed development.